Emotionally scarring both ways.
I guess that wasn't the BEST way to deal with a situation... But I suppose "giving him a taste of his own medicine," comes in order. I believe it was justified, but I also believe there is a much better way to justify this situation... Perhaps, turning him in?

The stepson ruined his daughter's life. If she can't trust her family, who can she trust and for how long? So, the father took it upon himself to ruin the stepson, I say that is still not enough for him. Now the girl is probably mentally unstable and the stepson who knows he committed wrong first deserved it. The girl didn't know why she got assaulted only that she trusted her brother. I have a little sister and the normal person doesn't even think about that sick crap. You're supposed to protect her from people, but now she can't trust anyone ever again. Terrible.